The objective of the proposed research is to understand how central neuronal populations generate patterns of activity that determine complex rhythmic behaviors. Our basic strategy for conducting neuroethological analyses involves (1) neurophysiological recordings from intact animals during normal behavior, (2) whole nerve cuff electrodes for simultaneous monitoring of large neuronal populations, (3) computer analysis to quantify population activity into unitary firing patterns, and (4) correlation of population activity in intact animals with subsequent intracellular recordings from individual members in progressively more reduced preparations. The centrally generated pattern to be analyzed is swimming in the marine gastropod, Aplysia brasiliana, a model preparation whose nervous system can be studied at the cellular level. Our published (von der Porten et al., 1979) and recent findings are compared with the general model of locomotion in other species. We will first correlate ongoing patterns of neuronal activity and behavior in the freely swimming animal and then reduce this animal to a semi-intact preparation in order to analyze the underlying cellular mechanisms. A major focus of the proposal is to improve our technique for computer analysis of multiunit spike trains, which has become a limiting factor in the sorts of the experiments that we can conduct. Our present technique (Camp and Pinsker, 1979) uses 2 recording channels to calculate amplitude and conduction velocity information to cluster unitary signals from different axons. This technique works well with background activity in quiescent animals but must be refined in order to analyze superimposed spikes characteristic of centrally generated patterns of neuronal activity. We are presently using this neuroethological approach to analyze small neuronal populations during simple behaviors such as siphon withdrawal (Kanz et al., 1979). We hope to extend this type of analysis to heightened neuronal activity in larger populations mediating a complex, rhythmic species-specific behavior.